The present invention relates to an image forming apparatus, such as an image forming apparatus using an electro-photographic method.
In an electro-photographic image forming apparatus, after images are formed on an image carrier, such as a photoconductor and an intermediate transfer body, the images are then transferred and formed as a permanent image on a transfer material, such as paper. When the speed of image formation is increased, or the image forming apparatus is downsized, the quality of the formed images tends to become degraded, because the images are distorted due to the vibration generated on a trailing edge of the transfer material due to high speed conveyance, which becomes a major problem.
Patent Documents 1 and 2 point out the above problem, and propose countermeasures.
That is, Patent Document 1 proposes a guide plate which softly presses a sheet of transfer material against the guide section to guide the transfer material to a transfer position.
Patent Document 2 proposes that an elastic guide member is assembled on an end of paired guide plates which guide the transfer material to the image transfer position, and that a free end of the guide member is folded at a predetermined angle.    [Patent Document 1] Unexamined Japanese Patent Application Publication No. 61-188,345    [Patent Document 2] Unexamined Japanese Patent ApplicationPublication No. 8-76,607
Degradation of the images due to the vibration of the trailing edge of the transfer material will now be detailed while referring to FIG. 1, which shows examples of the image degradation, as well as FIG. 4 which shows the transfer section of the image forming apparatus relating to the present embodiment.
In FIG. 4, transfer material P is conveyed by registration roller 23 to transfer position TR, which conducts a secondary transfer, and is structured of transfer section 7A and electrically grounded roller 61, whereby the toner images are transferred from intermediate transfer body 6 as permanent images onto transfer material P.
Paired guide plates 30 and 31, as rigid metal, guide transfer material P between registration roller 23 and transfer position TR.
When the trailing edge of transfer material P separates from upper guide plate 31, it tends to spring and vibrate so that toner dust particles are loosened, and misaligned image transfer occurs. The toner dust particles produce small points of toner on non-image area, as shown in FIG. 1(a), while the misaligned image transfer means slippage of the transferred image, as shown in FIG. 1(b). Such phenomena happen due to the high rigidity of thick transfer material P. In order to counter the phenomena, elastic extension guide member 32 is mounted on the end of upper guide plate 31, which decreases spring-up of the trailing edge of transfer material P, whereby the toner dust particles and the misaligned image transfer are effectively controlled.
The vibration control effects conducted by the elastic guide member are used in Patent Documents 1 and 2, the technologies of which can prevent degradation of the images on some level, however further problems as described below have occurred.
In recent years, high performance image forming apparatus, such as a color image forming apparatus, has been produced, and which has been used in various areas to produce various kinds of documents as well as documents for office use, and the types of the transfer materials have widely expanded. Further, due to the increased speed of the image formation, extension guide member 32 is strongly shocked by spring-up of the trailing edge of the transfer material, and extension guide member 32 tends to become damaged.
FIGS. 2(a) and 2(b) show examples of damaged extension guide member 32.
Extension guide member 32 is damaged when the trailing edge of the transfer material hits leading portion 32A of extension guide member 32, resulting for instance, as flipped end DF1 shown in FIG. 2(a), or cut edge DF2 shown in FIG. 2(b).
Due to the damage, extension guide member 32 can not exercise its guiding function well, which causes toner dust particles and misaligned image transfer, and also causes jamming of the transfer materials. Further, cut edge DF2 allows extension guide member 32 to bend easily. Bent extension guide member 32 abnormally approach the image carrier, and allows the image carrier to trigger an electrical discharge, which further results in distorted images.
Once the durability of extension guide member 32 is deteriorated, it is very difficult to stably produce high quality images for a long time, which of course becomes a major problem.
To solve this problem, the strength of extension guide member 32 can be increased, extension guide member 32 reduces control of the vibration of the transfer material, resulting in the generation of the toner dust particles and the misaligned image transfer.